The present invention relates to the field of magnetic data recording devices and, more specifically, to a flying magnetic head assembly for use with flexible magnetic data recording disks.
Flexible disk files commonly are used as peripheral mass digital data storage units in micro and minicomputer systems. A flexible disk file comprises a magnetic recording medium, in the form of a flexible or floppy disk, and a disk drive unit which spins the disk and records (writes)/reads data thereon with a magnetic transducer incorporated in a head assembly.
Commercially available 8, 51/4 and 31/2 inch flexible disk drives typically employ a button type of head assembly that makes contact with the magnetic recording layer coated on the disk. This is done to minimize the area of incident magnetic flux, thereby increasing linear bit density along the recording track.
Abrasive wear at the head/medium interface generally is not a problem. This is because specified data transfer rates can be achieved at modest disk rotational speeds (300 RPM or thereabout) and the linear bit density (typically 8-10 KPCi for commercially available disks) can be obtained with magnetic layers having a sufficient amount of resin and lubricants incorporated in the binder system to resist abrasion at these speeds.
However, with the rapid development of more powerful and faster computer systems, there is a pressing need to significantly improve the recorded bit density levels and data transfer rates of flexible disk files.
To obtain higher density, the magnetic recording layer will have to be much thinner and therefore more fragile. Also, the rotational speed of the disk will have to increase significantly to accommodate higher transfer rates.
Those skilled in the art will recognize that the combination of a more fragile recording layer and higher disk speed will present significant durability problems if the head assembly is designed to make frictional contact with the recording layer. A preferable approach is to bypass the wear problem by employing a non-contacting or "flying" head assembly that is separated from the disk surface by a submicron intervening lubricating air cushion or bearing. This approach is, of course, well known in the art of fixed or hard disk files which utilize flying heads.
The objective of a flying head system is to avoid contact between the head and medium so as to prevent damage to either but yet minimize head/disk spacing or "flying height" to maximize bit density. It is equally important that the head be stable in its flight and maintain a constant head/disk spacing in the interest of read/write reliability.
Although flying heads have been employed successfully in hard or rigid disk files, the aerodynamic design of such heads generally have been found inadequate for use with flexible disks. One reason for this is the substantial difference in the "flying environments".
In a hard disk drive, the magnetic recording layer is supported on a rigid metal base which does not deflect when subjected to pressure loads developed in the air bearing. This means the recording surface is maintained in a fixed and well defined plane that provides a stable flying environment.
On the other hand, the flexible disk has its magnetic layer supported on a compliant plastic film base and it tends to deform under pressure loading. Also, while it is intended that the plastic base be flat, in reality, flexible disks generally exhibit a small amount of warp or curl which may induce vibrations when the disk spins. Thus the flexible disk flying environment tends to be much more dynamic and complex. Other parameters that contribute to the complexity of the flexible disk flying environment include the stiffness of the medium; the response of the plastic base material to changes in temperature and humidity; the dynamic effects of the jacket or cassette in which the disk is enclosed; and head penetration and loading.
Flying head assemblies used with flexible disks typically comprise a support structure which mounts the read/write transducer with the transducer gap disposed on a compound curve (e.g. spherical) contoured face of the head that confronts the disk to establish the head/disk interface.
As is well known to those skilled in the art, in response to disk rotation, a thin layer of air adjacent to the recording layer surface is set in motion thereby establishing a Bernoulli effect air film which may serve as a lubricating air bearing between the head face and the recording surface.
Generally, the hydrodynamic resistance of the air film, which increases with rotational speed, is sufficiently large so that the head must be urged toward the disk with the application of an external force to reduce flying height to submicron levels (4) microinches and below) required for high density recording. This causes the air layer to be compressed and substantially increases pressure at the head medium interface. In response to the increased pressure, the flexible medium tends to dimple or buckle forming a dome at the interface that conforms somewhat to the curved contour of the head face. Often, to achieve low flying heights in the dome region the head is operated in a penetration mode wherein the face extends through the nominal plane of the recording surface and into the dome region.
It is preferable to minimize the loading force and amount of head penetration because at desirably low flying heights below 4 microinches because wear becomes an issue. At these very low flying heights unintentional contact may be made on an intermittent basis because of variations in coating thickness over the disk surfaces and/or variation in the plastic film base configuration which may be induced by changes in temperature and humidity or caused by manufacturing variances.
One approach, known in the prior art, to obtaining smaller disk/head spacing without increasing head loading is to selectively reduce pressure in the air bearing at the disk/medium interface by providing a pair of parallel slots which straddle the transducer gap and extend longitudinally along the face in a direction substantially parallel to the direction of media movement past the gap (along the track). For a representative example of a flying head with parallel slots used to reduce flying height relative to a flexible disk, reference may be had to U.S. Pat. Nos. 4,163,267; 4,330,804; 4,375,656; and 4,396,965.
Quantitively, the flying height characteristics of a head assembly is expressed in terms of the minimum spacing between the head face and disk surface. But it equally, if not more, important to examine this parameter qualitatively in terms of the area or zone of minimum spacing. If the area of minimum spacing (both in the radial and circumferential directions) is very small, the transducer must be precisely mounted on the support structure so that the gap is centered in the minimum spacing area to obtain the benefits of the low flying height. However, if the head is configured so that the area of minimum spacing is relatively large, manufacturing tolerances can be relaxed somewhat resulting in a substantial reduction in manufacturing cost.
In a paper entitled "Design of Low Flying Heads for Floppy Disk Recording", IEEE TRANSACTIONS ON MAGNETICS, Vol. Mag-20 No. 5, September 1984 by James A. White, the author discusses a computer model of the floppy disk/flying head interface. Simulations of spherical contour heads having a pair of parallel slots or a single transverse slot (perpendicular to the direction of media movement past the head) for ambient pressure relief at the interface are discussed. The results show both configurations produce very low clearances or flying height but neither produces a flat uniform clearance region (area of minimum spacing) in the vicinity of the spherical face apex where the transducer gap is normally located.
Therefore, it is a primary object of the present invention to provide a magnetic head assembly for use with a flexible magnetic disk that is characterized by its low flying height and relatively large area of minimum spacing.
Another object is to provide such a head assembly that exhibits these characteristics with relatively low head loading and penetration to minimize concern about head and/or disk wear.
Yet another object is to provide a magnetic head assembly for use with a flexible disk that exhibits desirable flying characteristics at head/disk spacings below 4 microinches.
Still another object is to provide such a head assembly which allows relaxation of gap position tolerances in the manufacturing process.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.